The present invention relates to a drive arrangement for a motor vehicle, having an internal combustion engine with a crankshaft which can be connected, via an interposed clutch, to a gearbox input shaft of a change-speed gearbox. An electric machine is provided in the drive arrangement and has a stator and a rotor.
Such a drive arrangement is disclosed, for example, by German reference DE 43 23 601 A1, in which a drive arrangement for a motor vehicle, in particular for a hybrid vehicle, is described. On account of the drive arrangement, which is constructed as above, the vehicle can be driven on the one hand by the internal combustion engine and on the other hand by the electric machine. The electric machine can also be activated, supporting the internal combustion engine, to drive the motor vehicle. Driving the vehicle by the electric machine alone is expedient, particularly in the range of low traveling speeds. However, in order then to make it possible to start up by means of the electric motor drive on its own, powerful electric machines are required which, on the one hand, have a large axial overall length and, on the other hand, are very costly.
In WO 98/40647, which, in relation to the first application on which priority is based, was published after the present application, a description is given of an electric machine integrated into a gearbox for motor vehicle internal combustion engines, and for the control thereof. Here too, the internal combustion engine can be connected, via a crankshaft and an interposed clutch, to a gearbox input shaft of a change-speed gearbox. Furthermore, an electric machine is provided which is switched via an intermediate gear mechanism in parallel with the gearbox input shaft. The intermediate gear mechanism is designed in the form of a step-up gear mechanism. As a result of the parallel arrangement of the intermediate gear mechanism, however, a relatively large amount of installation space is needed which, in particular from the point of view of passenger cars, is not available in the engine compartment thereof.
The electric machine described in WO 98/40647 can be designed as a so-called starter-generator. If the electric machine is switched as a starter motor, the internal combustion engine can be started thereby. When the internal combustion engine is in operation, it is possible to supply the on-board motor vehicle network via the electric machine switched as a generator. Starter-generators are normally slipped onto the crankshaft or the gearbox input shaft, so they must have the lowest possible space requirement.
On the basis of the above-mentioned prior art, the present invention is based on the object of developing a drive arrangement for a motor vehicle of the type mentioned at the beginning in such a way that the above-described disadvantages are avoided. In particular, it is intended to provide a drive arrangement which is particularly powerful and in which the production costs are reduced with respect to comparable drive arrangements. Furthermore, it is intended that the electric machine should also be designed to be particularly space-saving.
This object is achieved by a development of the drive arrangement mentioned at the beginning which, according to the invention, is defined by the fact that the electric machine, in order to step down its rotational speed, is operatively connected to the crankshaft and/or the gearbox input shaft via a step-down gear mechanism. The step-down gear mechanism is designed as an epicyclic gear mechanism which has a sun gear, an internal gear and a number of planet gears.
The drive arrangement designed in accordance with the invention makes it possible to circumvent the disadvantages described further above. If the electric machine is used, for example, as a starter-generator, the configuration according to the invention also makes it possible, even with relatively small electric machines, to produce such high torques when starting so that even the starting of large internal combustion engines is made possible. If the electric machine, for example, is used as an electric motor and is connected to the gearbox input shaft, it is made possible to start using the electric drive on its own with an acceleration response which is virtually identical in comparison to drive by the internal combustion engine. In this case, the overall axial length of the drive arrangement does not exceed a predetermined amount permitting transverse installation.
A basic idea of the present invention resides in the fact that the electric machine is operatively connected to the crankshaft and/or the gearbox input shaft via a separate step-down gear mechanism.
The use of an epicyclic gear mechanism as the step-down gear mechanism has proven to be particularly advantageous. Such an epicyclic gear mechanism can be arranged coaxially with the gearbox input shaft or with the crankshaft of the internal combustion engine. As a rule, epicyclic gear mechanisms have a sun gear, an internal gear and various planet gears, the individual gears being arranged and aligned coaxially with one another. In this way, an epicyclic gear mechanism constitutes a very effective gear mechanism with only a low space requirement.
The electric machine can advantageously be designed as a synchronous machine, especially a permanently excited synchronous machine, or as an asynchronous machine. The electric machine can be designed both as an external rotor type and as an internal rotor type. If an asynchronous motor is provided as the electric machine, its maximum rotational speed is around 10,000 rev/min. If the electric machine is designed as a synchronous motor, its maximum rotational speed lies in the range from 5000 to 10,000 rev/min. On the other hand, the maximum rotational speed of a modern internal combustion engine, especially of a diesel engine, lies in the range of 4000 rev/min. As a result of the measure of coupling the electric machine to the drivetrain via a step-down gear mechanism which steps down the rotational speed of the electric machine, the torque acting on the drivetrain from the electric machine is stepped up in such a way that the maximum permissible rotational speed of the electric machine is not exceeded. The torque which can be provided by the electric machine corresponds to a torque from a more powerful electric machine, which would take up many times the axial installation space. As a result of the drive arrangement according to the invention, the higher rotational speed of the electric machine can be stepped down by the step-down gear mechanism to the lower rotational speed of the internal combustion engine. At the same time, however, a high torque is transmitted.
The electric machine can be designed, for example, as an electric motor in a hybrid vehicle. The torque transmitted from the electric machine corresponds, inter alia as a result of the step-down gear mechanism, to a torque from a more powerful engine, in particular in the range of lower traveling speeds.
An electric machine which is particularly worth mentioning is, for example, also the starter-generator for vehicles. This is an electric machine whose rotor is mounted via the crankshaft mounting of the internal combustion engine. The starter-generator is used not only for starting and stopping the internal combustion engine but can also perform different functions during engine operation, such as supplying the on-board network with electrical energy (generator function), braking functions, booster functions, battery management, active vibration damping, synchronization of the internal combustion engine with the gearbox during change-speed operations, and the like.
The epicyclic gearbox can preferably be designed as a fixed-speed (fixed) epicyclic gear mechanism or as a clutch-operated or change-speed epicyclic gear mechanism.
In the following text, firstly some exemplary embodiments will be described in which a fixed-speed step-down gear mechanism is provided between engine and gearbox or, respectively, at the front end of the internal combustion engine, for the adaptation to an electric machine. In the further course of the description, exemplary embodiments will then also be described in which the step-down gear mechanism is designed as a change-speed/clutch-operated gear mechanism. However, the invention is not restricted to the exemplary embodiments described.
According to a preferred embodiment, the rotor of the electric machine can be operatively connected to the sun gear of the epicyclic gear mechanism, the sun gear meshing with planet gears mounted so as to be stationary. The planet gears in turn mesh with the internal gear that is operatively connected to the crankshaft or the gearbox input shaft. As a result, the internal gear can be driven by means of the electric machine.
In a further advantageous embodiment, provision is made for the rotor of the electric machine to be operatively connected to the sun gear of the epicyclic gear mechanism, the sun gear meshing with the planet gears. The planet gears in turn mesh with the internal gear which is fixed so that it cannot rotate (is stationary). The planet gears are rotatably mounted on a planet carrier (web pick-off), which is operatively connected to the crankshaft or the gearbox input shaft and is preferably permanently connected to the latter.
If an external rotor is used as the electric machine, it has proven to be advantageous to design the stator with an internal recess and in addition to provide the stator with a tooth system which points radially inward and forms the internal gear. With this configuration, a particularly compact arrangement of epicyclic gear mechanism and electric machine is possible.
An internal rotor type can advantageously be provided as the electric machine, the rotor of the electric machine being operatively connected so as to rotate with the sun gear of the epicyclic gear mechanism arranged parallel to the electric machine, preferably being permanently connected to the sun gear.
The planet gears can advantageously be rotatably mounted on protrusions which can be or are formed in one piece with a stator carrier. This permits a particularly compact arrangement of the step-down gear mechanism, and hence of the electric machine, to be provided.
In the following text, a design will be described in which the step-down gear mechanism can be switched or clutch-operated.
According to this preferred embodiment, the rotor of the electric machine can be operatively connected to the sun gear of the epicyclic gear mechanism, the sun gear meshing with planet gears which are rotatably mounted on a planet carrier. The planet carrier is operatively connected to the crankshaft or the gearbox input shaft. The planet gears also mesh with the internal gear, which is arranged so that it cannot rotate or can rotate, depending on the rotational speed of the sun gear.
In this embodiment, the epicyclic gear mechanism is operatively connected to the crankshaft or the gearbox input shaft via the planet carrier (web pick-off). The planet carrier is advantageously permanently connected to the shaft. Furthermore, the sun gear is connectedxe2x80x94preferably permanentlyxe2x80x94to the rotor of the electric machine. At a low rotational speed of the sun gear, for example during the starting of the electric machine, the internal gear is coupled so that it rotates with a component of the electric machinexe2x80x94for example the stator. Beginning at a specific rotational speed, the coupling is broken, so that the internal gear can then corotate with the planet carrier. A coupling is then produced between the internal gear, the planet gears arranged on the planet carrier, and the sun gear.
The change-speed/clutch-operated step-down gear mechanism can preferably have at least two step-down ratios.
The epicyclic gear mechanism can advantageously have one or more, preferably two, clutches, via which it is or can be clutch-operated or its speed is or can be changed. The clutches may be designed radially or axially as friction clutches, multi-plate clutches or the like. For example, the clutch or the clutches can be designed as multi-plate clutches adjusted via toggle levers, as clutches which can be operated magnetically, mechanically, electrically, pneumatically or hydraulically, as centrifugal clutches or the like. The invention is not restricted to specific clutch types, so that other clutch types are also conceivable and possible.
The clutch or the clutches can advantageously be switched or operated as a function of the temperature and/or the rotational speed or the like. In the case of cold starting of the internal combustion engine, for example, a high starting torque is required, for which reason the step-down ratio has to be activated with the aid of the step-down gear mechanism (epicyclic gear mechanism). On the other hand, activation of the step-down gear mechanism during warm starting of the internal combustion engine is not necessary, because of the lower starting torque needed.
In a preferred embodiment, the clutch or the clutches is/are designed as centrifugal clutches, however.
For this purpose, the clutch or the clutches can advantageously have a spring pot, a compression spring and a piston.
If a plurality of clutches are used in the epicyclic gear mechanism, these can be connected to one another via a coupling element. Such a coupling element may be, for examplexe2x80x94but not exclusivelyxe2x80x94, a leakage or the like. The coupling element achieves the situation in which, when one clutch is operated, the other clutch is also operated automatically.
In a particularly preferred embodiment, a change-speed/clutch-operated epicyclic gear mechanism is proposed for stepping down the electric machine, and is permanently connected to the crankshaft at the planet carrier (web pick-off), and to the sun gear at the rotor of the electric machine. During starting, the internal gear is coupled via a suitable clutch to the housing of the internal combustion engine or the housing of the change-speed gearbox, in such a way that it is initially arranged so that it cannot rotate. Beginning at a specific rotational speed (for example 500 rev/min), this first coupling is broken and, as far as possible at the same time, a second coupling between the internal gear and the sun gear and the planet carrier is produced. During starting, up to about 500 rev/min, a step-down ratio of about 3 to 5 is thus provided, and beginning at 500 rev/min, the rotor is coupled rigidly to the crankshaft. The execution of the couplings/change-speed elements can be controlled by centrifugal force (centrifugal clutch) or as a result of the actuation of electromagnets or other elements.
The electric machine can advantageously be arranged between the internal combustion engine and the change-speed gearbox or at the front end of the internal combustion engine.
As a rule, the electric machine will be provided between the internal combustion engine and the change-speed gearbox. In this case, it may be operatively connected either to the crankshaft of the internal combustion engine or to the gearbox input shaft of the change-speed gearbox. However, applications are also conceivable in which the electric machine is arranged at the front end of the internal combustion engine. In this case, the electric machine is operatively connected only to the crankshaft of the internal combustion engine. In the last-mentioned case, it is possible for the electric machine to be connected, for example via the rotor, to the pulley of the internal combustion engine. Other ancillary units can then also be driven by this pulley on the rotor.
At least one torsional vibration damper can advantageously be provided in the epicyclic gear mechanism. If such a torsional vibration damper is integrated in the epicyclic gear mechanismxe2x80x94for example in the planet carrierxe2x80x94vibration damping in the individual structural elements can be achieved in this way. If the electric machine is arranged between the internal combustion engine and the change-speed gearbox, it is possible, for example, for vibration damping in the drivetrain or in the clutch to be implemented via the vibration damper, for example with regard to a two-mass flywheel. If the electric machine is arranged at the front end of the internal combustion engine, it is possible, for example, for vibration damping or torsional damping of the belt drive to be achieved via the vibration damper.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of the disclosure. For a better understanding of the invention, its operating advantages, and specific objects attained by its use, reference should be had to the drawing and descriptive matter in which there are illustrated and described preferred embodiments of the invention.